Method of preparing {62 -methyl adipic acid

ABSTRACT

In the process of producing Beta -methyl adipic acid from a mixture of para and meta methylcyclohexanol by oxidation with nitric acid for a time and at a temperature sufficient for production of the Beta -methyl adipic acid, and cooling of the reaction product for precipitation of the Beta -methyl adipic acid and formation of a mother liquor, the improvement which comprises utilizing in the reaction as the source of para and meta methylcyclohexanol a hydrogenated crude cresol mixture which contains as well as para and meta methylcyclohexanol, up to 20 percent of ortho methylcyclohexanol or cyclohexanol or ortho methylcyclohexanol and cyclohexanol.

United States Patent Strickrodt et al.

[ METHOD OF PREPARING B-METHYL ADIPIC ACID [72] lnventorsi JorgStrickrodt, Laatzen; Gotthard Engemann, Salzgitter-Bad; Hans- GerdEulenhofer, Salzgitter-Lebenstedt, all of Germany [73] Assignee:Veba-Chemie Nord GmbH, Gelsenkirchen-Buer, Germany [22] Filed: March 13,1970 [21] Appl. No.: 19,494

[30] Foreign Application Priority Data April 26, 1970 Germany ..P 19 21441.6

[52] US. Cl. ..260/531 R, 260/537 P [51] Int. Cl ..C07c 55/04 [58] Fieldof Search ..260/531 R, 537 P [56] References Cited UNITED STATES PATENTS2,300,955 11/1942 Mier ..260/531 R [151, 3 0 1, {451 Dec. 12, 1972FOREIGN PATENTS OR APPLICATIONS 1,205,516 11/1965 Germany ..260/531 R265,959 12/1927 United Kingdom....260/531 R Primary Examiner-Lorraine A.Weinberger Assistant Examiner-Richard D. Kelly AttorneyBurgess, Dinklage& Sprung [57] ABSTRACT liquor, the improvement which comprises utilizingin the reaction as the source of para and meta methylcyclohexanol ahydrogenated crude cresol mixture which contains as well as para andmeta methylcyclohexanol, up to 20 percent of ortho methylcyclohexanol orcyclohexanol or ortho methylcyclohexanol and cyclohexanol.

5 Claims, No Drawings METHOD OF PREPARING B-METHYL ADIPIC ACID Thesubject of this invention is a process for preparing B-methyl adipicacid of great purity from a methylcyclohexanol mixture which may alsocontain cyclohexanol.

From Example 1 of DAS No. 1,205,516 it is known that a very pureB-methyl adipic acid is obtained from a mixture of m methylcyclohexanoland p-methylcyclohexanol by oxidation with nitric acid. As it is statedin. said Auslegeschrift, however, either pure pmethylcyclohexanol or amixture of p-methylcyclohexanol and m-methylcyclohexanol containing nomore than 70 percent of the meta compound must be used in order toobtain B-methyl adipic acid.

The starting substance for the preparation of B- methyl adipic acidaccording to the invention is the methylcyclohexanol mixture that isproduced by the hydrogenation of crude cresol from the processing oftar. Often this methylcyclohexanol mixture still contains cyclohexanol,because the separation of phenol from the cresols can be difficult.Since the distillative breakdown of crude cresol into mand p-cresol onthe one hand and o-cresol on the other is technically very complicatedand expensive, it appeared desirable to use the substantially cheapercrude cresol as the startin g material for the process of the invention.

The process of the invention for the preparation of B- methyl adipicacid from a methylcyclohexanol mixture by oxidation with aqueous nitricacid, cooling the oxidation mixture and separating the precipitateddicarboxylic acid is characterized in that a hydrogenated crude cresolmisture which may contain up to 20 percent o-methylcyclohexanol andcyclohexanol is used as the starting material.

In this process, a portionof the mother liquor that is produced can belet out and restored to a nitric acid content of 50 to 70 percent byconcentration and/or by the addition of highly concentrated nitric acid,and can be returned to the reaction process.

Preferably the oxidation of the methylcyclohexanolcyclohexanol mixtureis performed continuously.

The process of the invention, therefore, starts with hydrogenatedcommercial crude cresol obtained by the hydrogenation of commercialcrude cresol containing mand p-cresol and up to 20 percent o-cresol orup to 20 percent o-cresol and phenol, or up to 20 percent phenol. Thehydrogenated crude cresol of the said composition is oxidized with 50 to70 percent nitric acid solution, with or without the addition of acatalyst, at a suitable temperature, which can be 50 to 75 C, preferably60 to 70 C, e.g. at 60 C. After the mixture is cooled, for example to lto +25 C, a nearly pure B-methyl adipic acid having a melting point of95 C precipitates. The compound was identified by the dianilide,according to W. Markownikoff in Liebigs Annalen, No. 336, p. 302 1904).Surprisingly, the adipic acid that forms in the oxidation does notprecipitate when the starting material according to the invention isused and the stated working conditions are maintained,

although it is more poorly soluble in the nitric acid used for theoxidation than ,B-methyl adipic acid. This is attributed to the mannerin which the solubility is affected by short-chain carboxylic acidswhich develop as by-products.

If cooling to +1 0 C is performed as stated above, a very pure B-methyladipic acid separates in a yield of about 60 percent with reference tothe starting mixture of mand p-methylcyclohexanol. As previously stated,the mother liquor is restored to a content of 50 to percent l-lNO eitherby concentrating it or by the addition of anhydrous nitric acid, and itis returned to the oxidation process. Since, however, the adipic acidformed from o-methylcyclohexanol and cyclohexanol concentrates in themother liquor, a portion of the mother liquor has to be purged. If thispurged portion is processed for ,B-methyl adipic acid, the yieldincreases from 60 to 91 percent on the basis mentioned above.

EXAMPLE 1 57 g of a hydrogenated commercial cresol'mixture (76 percentp-methylcyclohexanol, 12 percent mmethylcyclohexanol and 12 percento-methylcyclohexanol and cyclohexanol) were added, with stirring, to154.1 g of 66 percent nitric acid containing 0.16 wt. percent ofammonium vanadate and 0.4 wtQpercent of copper sulfate, over a period of30 minutes in such a manner that a reaction temperature between 60and 65C was established. After the addition of the alcohol had ended, themixture was allowed to react for another half hour, and then it wascooled to 10 C. As soon as crystallization was complete, the mixture wasfiltered, 40.3 g of B-methyl adipic acid being obtained, equal to 57.2percent of the theory with reference to mand p-methylcyclohexanol.

' Acid number: 703

Melting point C.

The mother liquor obtained in the experiment was concentrated in vacuoand restored to the initial 66 percent concentration with 96 percentnitric acidsolution. By the use of this mother liquor under theconditions described above (i.e. using this liquor as the nitric acid inthe main reaction), the yield of B-methyl adipic acid was increased to64 g 91 percent.

EXAMPLE 2 The oxidation was performed continuously, the circulation ofthe acid between a reactor, a degasser and a cooler being accomplishedby the driving action resulting from the production of gases. In largerapparatus the use of a circulating pump would be advisable. 750 g ofmethylcyclohexanol mixture plus 2 kg of 67 percent nitric acidcontaining 0.1 percent of the catalyst mixture used in Example 1, wereinjected hourly through nozzles into the reactor. An aliquot portion ofthe product was continuously withdrawn ahead of the cooler through aseparate cooler. The oxidation solution was cooled to 10 C and theB-methyl adipic acid that separated was removed by filtration.

In this experiment a different commercially available hydrogenatedcresol mixture was used, which consists of 50 percentp-methylcyclohexanol and 34 percent mmethylcyclohexanol, plus 16 percentcyclohexanol and o-methylcyclohexanol. 505 g per hour of ,B-methyladipic acid were obtained, which corresponds to a 7 yield, withreference to mand p-methylcyclohexanol,

of 57 percent.

The process can be operated with recycling. The

' mother liquor was concentrated by evaporation. 25

percent of the concentrated liquor was purged and the cyclohexanol andcyclohexanol containing up to percent of ortho methyicyclohexanol orcyclohexanol or ortho methylcyclohexanol and cyclohexanol, obtained byhydrogenation of a crude cresol mixture derived from tar, with nitricacid at a temperature of 50 to 75 C. in the presence of ammoniumvanadate -copper sulfate catalyst, to produce a reaction liquorcontaining B- 4 methyl adipic acidandadipic acid;

b. cooling the reaction liquor to 10 C to precipitate B-methyl adipicacid and form a mother liquor containing adipic acid. I

I 2. Process according to claim 1, wherein the precipitated reactionproduct is removed from the mother liquor, the mother liquor containsnitric acid and part of the mother liquor is recycled for use in theoxidation reaction.

3. Process according to claim 1, said crude cresol mixture containing12-20 percent of ortho methylcyclohexanol and cyclohexanol.

4. Process according to claim 1, the precipitated beta methyladipic acidhaving an acid number of 703 and a melting point of C.

5. Process according to claim 1, said B-methyl adipic acid being nearlypure, having a melting point of about 95 C.

2. Process according to claim 1, wherein the precipitated reactionproduct is removed from the mother liquor, the mother liquor containsnitric acid and part of the mother liquor is recycled for use in theoxidation reaction.
 3. Process according to claim 1, said crude cresolmixture containing 12-20 percent of ortho methylcyclohexanol andcyclohexanol.
 4. Process according to claim 1, the precipitated betamethyladipic acid having an acid number of 703 and a melting point of95* C.
 5. Process according to claim 1, said Beta -methyl adipic acidbeing nearly pure, having a melting point of about 95* C.